1. Field of the Invention
The present invention relates to a system for controlling the aerodynamics of a ground vehicle. More specifically, the present invention relates to a system that efficiently blows air into the trailing suction area, to improve the aerodynamics of the ground vehicle and a trailing edge treatment.
2. Problems in the Art
All objects that move through air will encounter resistance that increases markedly with speed. Even though it greatly affects all land vehicles, air resistance is most difficult to manage in the trucking industry. Automobiles can be streamlined. Buses can be streamlined. Trains can be streamlined. Almost any vehicle can be streamlined and this is the most efficient way of reducing air resistance. However, trucks are difficult to streamline due to the boxy nature of the trailer that carries the cargo. Increased air resistance translates to inefficient movement, increased fuel consumption, and increased transportation cost.
Recently there has been progress with streamlining the frontal area of the truck. Notably, almost all new semi tractor-trailer trucks have a wind deflector, incorporated above the cab, that directs the air up and over the trailer as the truck moves along the road, these wind deflectors have done much to streamline the front of semi tractor-trailer trucks. Smaller straight trucks are beginning to use a “nose cone” type of wind deflector on the front of the trailer, above the cab. This device eliminates the flat frontal surface and permits limited streamlining. Efforts to streamline the frontal areas around the fenders, gas tanks, and below the front bumper have also helped reduce moving air resistance.
Side wind problems also increase forward air resistance. If a sideway wind blows between the cab and the trailer, and replaces the decreased air pressure area between the cab and the trailer in a semi tractor-trailer truck, this increased air pressure area mimics the wind resistance problem of trying to push a flat trailer front against the oncoming forward air resistance. Skirts extending backwards from the cab, between the cab and the trailer, help to block the side wind problem. Truckers also try to minimize the size of the space between the cab and the trailer if they have adjustment capability in the fifth wheel connector. Sideway wind also causes problems below the trailer in the wheel-area undercarriage. Skirts extending down below the trailer sides, to cover the wheel-area undercarriage, are used to minimize side wind problems in this area. These skirts have gained limited acceptance, possibly due to concerns about increased risk of tipping sideways in very high side winds.
The sides and tops of the trailers have also been smoothed to minimize moving air resistance. U.S. Pat. No. 5,000,508 by Woods (Wind Drag Reduction Device for Vehicles) discusses a drag reduction unit that comprises an inflatable shell, on the roof of the trailer that has rounded corners and a flat upper surface to reduce air drag; it has applications in open-top trailers. The Bernoulli effect at speed inflates it.
Streamlining the frontal, top, and side areas has reduced forward moving air resistance, helping the trucking industry's concern with air resistance that causes inefficient movement, increased fuel consumption, and increased transportation cost. Streamlining cannot eliminate all air resistance. The large frontal area still creates an area of high-pressure air in front of the moving truck. There is also a low-pressure vacuum-like “suction” area behind the moving truck (trailer), which pulls it backward and slows forward progress. The suction is due to the pressure differential between the large front pressure wave and the large vacuum-like area of lower pressure behind the trailer. This area of lower pressure is generated by the truck's (and trailer's) passage through the air, creating a void behind it. Raising the air pressure in the vacuum-like “low pressure wake” will increase the pressure behind the truck, which will reduce the pressure differential, thereby reducing the suction drag intensity. Reducing the size of the height and width dimensions of the “low pressure wake” (vacuum) would also result in a decreased drag magnitude. There have been attempts to modify the size and intensity of the vacuum-like suction drag area behind the trailer on a moving truck.
U.S. Pat. No. 5,908,217 by Englar (Pneumatic Aerodynamic Control and Drag-Reduction System for Ground Vehicles) proposes using a compressor to discharge small amounts of air at the rear portion of the vehicle. Numerous sensors and valves enable rolling and yawing moments to supplement control of aerodynamics. It requires energy to power the system which compromises overall system efficiency and complicates the suction drag solution with maintenance considerations.
U.S. Pat. No. 5,280,990 by Rinard (Vehicle Drag Reduction System) suggests a vehicle drag reduction system of many components. It has a vehicle-mounted nosecone, deflecting air between the trailer and the tractor. Trailer side skirts for the undercarriage area are also included. Previously discussed, the nose cone, and to some extent, the side skirts have some success in the industry. Vertical vanes that scoop and deflect air sideways behind the truck help to manage rear suction drag. The vertical air scoop vanes are mounted at the rear corners by spring biased supports, to allow opening rear doors and restoring the deflecting positions upon closing. However, because trucks often back up to a dock to load and unload from the rear of the trailer, using doors that open to the full trailer dimension, modifications to this area have met with limited acceptance. Transverse upper and lower scoops deflect air up and down the rear surface. Both scoops are fabricated from a resilient material to allow compression against a loading dock structure. Both the rear scoops and vertical vane deflectors create a significant wind drag profile of their own to overcome the suction drag, creating questionable benefits and acceptance.
U.S. Pat. No. 5,348,366 by Baker (Drag Reduction Device for Land Vehicles) consists of large rectangular plates mounted to the after-end of a truck trailer. The plates are smaller than the trailer cross-section and are supported by hinged truss assemblies on the truck frame. The plates are parallel to the truck trailer's rear end. While the vehicle is moving, a vortex becomes locked between the rear of the trailer and the plates, creating a low-pressure region. The suction created changes air flow patterns behind the vehicle to reduce drag. The device is retractable to permit loading.
U.S. Pat. No. 6,257,654 B1 by Boivin (Air Drag Reduction Apparatus) incorporates a vertical plate boat-tail system behind the rear of the trailer that is moved when the doors open. In a way, this and the preceding systems are both a type of boat-tail as they do not require energy input or create additional drag. However, trucker acceptance depends upon the trucker's willingness to relocate the rear-plate systems before backing to load or unload.
Therefore, prior art systems are inconvenient or consume significant energy of their own to operate, minimizing benefit. There is a need for a rear drag reduction system that does not require expending energy running a compressor, or expending energy creating significant additional drag in the process. There is also a need for a rear drag reduction system that does not require the inconvenience of relocating behind-the-trailer wind deflection plates.